w w ap eP m e tr .X w om .c s er UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Subsidiary Level and Advanced Level * 1 9 1 8 9 8 9 7 3 9 * 9700/31 BIOLOGY Advanced Practical Skills 1 May/June 2011 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions. READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name on all the work you hand in. Write in dark blue or black ink. You may use a pencil for any diagrams, graphs or rough working. Do not use red ink, staples, paper clips, highlighters, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Answer all questions. You may lose marks if you do not show your working or if you do not use appropriate units. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 2 Total This document consists of 11 printed pages and 1 blank page. DC (CW/DJ) 31753/6 © UCLES 2011 [Turn over 2 You are reminded that you have only one hour for each question in the practical examination. You should: • Read carefully through the whole of each question. • Plan your use of the time to make sure that you finish all the work that you would like to do. You will gain marks for recording your results according to the instructions. 1 Enzyme E catalyses the hydrolysis of starch to glucose. The end-point of the reaction can be found by measuring the time taken for all the starch to be hydrolysed. You are required to investigate the effect of the independent variable, copper sulfate concentration, on enzyme E. You are provided with: labelled contents hazard concentration /% volume / cm3 E amylase solution irritant 1 10 S starch solution none 1 50 C copper sulfate solution harmful irritant 0.03 20 W distilled water none – 100 iodine iodine in potassium iodide solution irritant – 50 Copper sulfate can inhibit enzyme E. The extent of inhibition depends on the concentration of the copper sulfate solution. A student investigated the inhibition of enzyme E at concentrations of copper sulfate solution greater than 0.03% and found that the enzyme was completely inhibited. The student suggested the hypothesis: concentrations of copper sulfate solution below 0.03% will continue to inhibit the enzyme. You are required to investigate this hypothesis by carrying out a serial dilution of copper sulfate solution which reduces the concentration by ten-fold between each successive dilution. © UCLES 2011 9700/31/M/J/11 For Examiner’s Use 3 Fig. 1.1 shows how to make the first concentration of 0.003% copper sulfate solution. For Examiner’s Use 9 cm3 of distilled water, W 1 cm3 of copper sulfate solution, C 10 cm3 of 0.03% copper sulfate solution, C 0.003% copper sulfate solution ................... ................... Fig. 1.1 (a) (i) Complete Fig. 1.1 to show how you will make two further concentrations of copper sulfate solution. [3] Proceed as follows: 1. Prepare the concentrations of copper sulfate solution as shown in Fig. 1.1 in the containers provided. Use the syringe labelled ‘For copper sulfate’. 2. Label test-tubes with the concentrations of copper sulfate solutions and label another test-tube W. 3. Wipe the tile clean with a damp paper towel and then dry the tile. Label the tile, as shown in Fig. 1.2. The numbers indicate the sampling times in seconds. drop of iodine 15 30 45 60 75 90 105 120 135 150 165 180 Fig. 1.2 4. Put one drop of iodine on the tile at each sampling time, as shown in Fig. 1.2. 5. Put 1 cm3 of W into the labelled test-tube. © UCLES 2011 9700/31/M/J/11 [Turn over 4 6. Put 3 cm3 of S into the same test-tube. Mix well. 7. Put 0.5 cm3 of E into the same test-tube. Mix and start timing. 8. Use a glass rod to stir the mixture. 9. After 15 seconds use the glass rod to transfer a drop of the mixture to the iodine drop, labelled 15, on the tile. 10. Immediately clean the glass rod with a paper towel. 11. Repeat steps 8 to 10 at 15 second intervals until the iodine drop does not change colour. If the iodine drop changes colour at 180 seconds, record ‘more than 180’ as your result (for step 12). 12. Record the time taken to reach the end-point. 13. Repeat steps 3 to 12 replacing the 1 cm3 of W with 1 cm3 of the lowest concentration of copper sulfate solution. 14. Repeat step 13 with the other concentrations of copper sulfate solution. © UCLES 2011 9700/31/M/J/11 For Examiner’s Use 5 (ii) Prepare the space below and record your results. For Examiner’s Use [5] (iii) The student’s hypothesis stated that “concentrations of copper sulfate solution below 0.03% will continue to inhibit the enzyme”. Explain how your results provide evidence for the support or the rejection of this hypothesis. ................................................................................................................................. ................................................................................................................................. ................................................................................................................................. ................................................................................................................................. © UCLES 2011 ............................................................................................................................. [2] 9700/31/M/J/11 [Turn over 6 (iv) Identify one significant source of error in your investigation. ................................................................................................................................. ............................................................................................................................. [1] (v) A colorimeter could have been used to determine the end-point. Describe three other modifications to this investigation which would improve the confidence in your results. ................................................................................................................................. ................................................................................................................................. ................................................................................................................................. ................................................................................................................................. ................................................................................................................................. ................................................................................................................................. ............................................................................................................................. [3] Table 1.1 shows the results of an investigation into the effect of the concentration of copper sulfate solution on a protein suspension. A protein suspension was mixed with different concentrations of copper sulfate solution. After a set time, the percentage absorbance of light was measured using a colorimeter. Table 1.1 copper sulfate concentration / mol dm–3 × 10–3 trial 1 trial 2 trial 3 trial 4 trial 5 mean 25.0 100 99 100 99 100 100 12.5 97 95 80 97 94 96 5.5 78 81 79 82 80 80 3.5 84 59 58 58 62 1.5 9 11 10 9 8 (b) (i) © UCLES 2011 absorbance of light by protein suspension / % 9 Draw a circle around each of the anomalous results and complete the table. 9700/31/M/J/11 [2] For Examiner’s Use 7 (ii) Plot a graph of the data shown in Table 1.1. For Examiner’s Use [4] (iii) Explain the effect of copper sulfate solution on the protein suspension. ................................................................................................................................. ................................................................................................................................. ................................................................................................................................. ................................................................................................................................. ............................................................................................................................. [2] [Total: 22] © UCLES 2011 9700/31/M/J/11 [Turn over 8 2 J1 is a slide of a stained transverse section through a leaf. For Examiner’s Use Fig. 2.1 (a) Draw a large plan diagram of the part of the leaf indicated by the shaded area in Fig. 2.1. Label the xylem and an air space. [5] © UCLES 2011 9700/31/M/J/11 9 (b) Make a large drawing of six cells from the part of the leaf indicated by the shaded area in Fig. 2.2. For Examiner’s Use The cells should be two adjacent (touching) cells from the epidermis and two adjacent cells from each of the next two layers. Fig. 2.2 Label one epidermal cell. [5] © UCLES 2011 9700/31/M/J/11 [Turn over 10 Fig. 2.3 is a photomicrograph of a transverse section through a leaf of a different plant species. Y Fig. 2.3 (c) The actual length of line Y is 785 μm. Use this measurement to calculate the magnification of Fig. 2.3. You may lose marks if you do not show your working or if you do not use appropriate units. magnification × .................................................. [3] © UCLES 2011 9700/31/M/J/11 For Examiner’s Use 11 (d) Prepare the space below so that it is suitable for you to record the observable differences between the specimens on J1 and in Fig. 2.3. Record your observations in the space you have prepared. [5] [Total: 18] © UCLES 2011 9700/31/M/J/11 For Examiner’s Use 12 BLANK PAGE Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. University of Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge. © UCLES 2011 9700/31/M/J/11